In manufacturing process of an integrated circuit (IC) chip, it is one of the most important processes to expose and transfer a design pattern of a chip onto a photoresist on the wafer surface, which is performed with an apparatus called lithography machine (exposure machine). The resolution and exposure efficiency of the lithography machine has a significant impact on the characteristic line width (i.e., the resolution) and production rate of the IC chip. And, as a critical system of the lithography machine, the motion precision and process rate of the wafer ultra-precision motion positioning system (hereinafter abbreviated as wafer stage), can largely determine the resolution and exposure efficiency of the lithography machine.
FIG. 1 illustrates the main principle of a step-and-scan projection lithography machine. Deep ultra-violet light from a light source 45 transmits through a mask 47 and lens 49 and projects a certain portion of the pattern of the mask onto a specific chip of the wafer 50, wherein the motions of the mask and the wafer are in opposite directions and are synchronized according to a specific speed ratio, and finally, the whole pattern on the mask is transferred onto the corresponding chip of the wafer.
The main function of the wafer stage motion positioning system is to move, with the wafer held thereon, in the exposure process at a preset speed and in a preset direction in order to allow precise transfer of the mask pattern onto various parts of the wafer. Due to the small line width of the chip (presently, the minimum line width has reached 45 nm), in order to guarantee the precision and resolution of the lithography, the wafer stage is required to have a very high moving and positioning accuracy; since the productivity of the lithography is determined largely by the motion speed of the wafer stage, for improvement of productivity, there is an increasing demand for improving the motion speed of the wafer stage.
FIG. 2 is a structural schematic diagram of a wafer support platform of a lithography machine in the related art. The wafer support platform 16 includes a coarse motion module 18 and a fine motion module 20. Each of the coarse motion module 18 and the fine motion module 20 has a stationary part, a movable part and a driving part. A stationary part 8 of the coarse motion module 18 is connected to a base stage 30. The movable part of the coarse motion module 18 is movable relative to the stationary part. A stationary part 12 of the fine motion module 20 is connected to the movable part 10 of the coarse motion module 18. A movable part 14 of the fine motion module 20 is movable relative to the stationary part 12. The wafer support platform 16 is configured to support a wafer W, and the wafer W is not a part of the wafer support platform. Herein, the “stationary part” is a concept defined with respect to the movable part, and the “stationary part” itself can also be movable. It is well known that the driving motor for the coarse motion module may be a linear motor, etc., and the driving motor for the fine motion module may be a planar motor, a voice coil motor, etc.